1. Field of the Invention
The present invention relates to a base station, a radio resource control equipment, a mobile station, a communication system, and a communication method.
2. Description of the Related Art
When transmitting packets of information such as a voice and a moving picture, having a short acceptable delay time, it is important to guarantee the acceptable delay time.
For the above purpose, for example, a base station has heretofore given priority to packets transmitted by a mobile station in consideration of the acceptable delay time, and performs scheduling that controls the order of transmitting packets in accordance with priority. To be more concrete, the base station has previously defined the acceptable delay time of packets in accordance with the type of information. Then, the base station has obtained a difference between the defined acceptable delay time and an elapsed time from the generation of packets to the present. The base station has defined a packet having the smallest difference as a packet having the highest priority. In this case, the packets are sequentially transmitted from the one having the smallest difference between the acceptable delay time and the elapsed time. Besides the above, a router has also carried out another type of scheduling that controls to transmit a packet having a higher priority indicated by the DSCP prior to a packet having a lower priority, based on the DSCP (DiffServe Code Point).
Moreover, in order to guarantee the acceptable delay time, the base station has sometimes performed a fixed allocation of radio resources, in which a radio channel is divided into a plurality of time slots, and the time slots are fixedly allocated to mobile stations. In this case, the base station has fixedly allocated time slots necessary to transmit information having short acceptable delay times to mobile stations transmitting the packets of such information. FIG. 1 shows the case where the base station fixedly allocates the uplink packet channel 307 to a mobile station of a user #1 and a mobile station of a user #2.
Each of the frames 309a to 309c is composed of eight time slots. Each time slot 307b composed of two (the fourth and fifth) slots is fixedly allocated to the user #1 in order to transmit any of the real time packets 381b and 383b of the information having a short acceptable delay time. Each time slot 307a composed of three (the first to third) slots is fixedly allocated to the user #2 in order to transmit any of the real time packets 381a, 382a and 383a. Each time slot 307c composed of residual three slots is shared by the user #1 and the user #2 in order to transmit the non-real time packet 308 of information having a long acceptable delay time.
However, in the case of performing the scheduling, the mobile stations and the base station, which transmit and receive the packets always need to be aware of information concerning the priorities of packets stored in the buffers of the mobile stations and the elapsed time necessary to acquire the priorities for the purpose of controlling the transmission sequence of the packets. Therefore, the mobile stations and the base station must always transmit/receive and be aware of information concerning the priorities, the elapsed times and the like for all the packets. Consequently, in the scheduling, there has been a problem that a control time for controlling the sequence is increased with increases a control delay, resulting in an inability to satisfy the acceptable delay time to be required. Moreover, there has been another problem in that overheads are increased.
Moreover, in the case of performing the fixed allocation of radio resources, a certain quantity of radio resources are fixedly allocated irrespective of the quantity of radio resource necessary for each mobile station to actually transmit the packets. Accordingly, there has been a problem in that a situation frequently occurs, in which the actual necessary quantity of radio resources is much smaller than the quantity of radio resource fixedly allocated, leading to a large waste of the radio resources. Specifically, there has been a problem in that each mobile station reserves too much radio resources, thus causing radio resources not to be used efficiently.
For example, in FIG. 1, a certain slot number of time slots 307a and 307b are fixedly allocated regardless of the number of the real time packets 381a to 383a, 381b and 383b transmitted by the mobile stations of the respective users. However, in the second frame 309b, the user #2 uses only one slot in order to transmit the real time packet 382a. Moreover, the user #1 does not use the allocated time slot 307b at all since the user #1 transmits no transmission packet. As a result of this, the slots 2 and 3 allocated to the user #2 and the slots 4 and 5 allocated to the user #1 are wasted, thus deteriorating the utilization efficiency of radio resources.
Furthermore, there has been a case in which the fixed allocation of radio resources cannot cope with a case where a required transmission rate varies in accordance with a change in an image, for example, such as a moving picture, and thus the acceptable delay time cannot be satisfied. Then, the base station has allocated radio resources to the mobile stations in response to the maximum transmission rate in order to solve the problems described above. Consequently, there has occurred a problem that the wasted radio resources increase even further leading to further deterioration of the utilization efficiency of radio resources. Moreover, in order to allocate radio resources in response to the maximum transmission rate, the transmission rate needs to be clear and that the transmission rate needs to be aware by the lower layer. Therefore, the method for allocating radio resources in response to the maximum transmission rate cannot be employed for general-purpose applications, and thus the acceptable delay time cannot be satisfied in some cases.
Accordingly, it is desirable to provide a base station, radio resource control equipment, a mobile station, a communication system and a communication method, which are capable of satisfying the acceptable delay time required for the packets, and enabling the radio resources to be used efficiently.